Abstract: This study uses automobile insurance loss costs as a proxy for tort system costs under contributory and comparative negligence standards. The principal finding is that insurance consumers in states that have adopted comparative negligence pay more for automobile liability insurance than do consumers in states that retain traditional contributory negligence. States that have adopted "pure comparative" negligence standards exhibit absolute higher costs than do states that have adopted "modified comparative" negligence standards, and both have higher costs than states that have retained contributory negligence. Moreover, when population density, accident fatalities, and no-fault insurance are allowed for, the average annual dollar loss cost increases are highest with pure comparative and lowest with contributory. To the extent that automobile insurance losses are an accurate proxy for the entire negligence and liability system, states with comparative negligence will have higher liability costs than will those with contributory negligence.